--- a/dom/base/Element.cpp
+++ b/dom/base/Element.cpp
@@ -1316,16 +1316,53 @@ Element::GetAttribute(const nsAString& a
       // See bug 232598
       // aReturn is already empty
     } else {
       aReturn.SetNull();
     }
   }
 }
 
+bool
+Element::ToggleAttribute(const nsAString& aName,
+                         const Optional<bool>& aForce,
+                         nsIPrincipal* aTriggeringPrincipal,
+                         ErrorResult& aError)
+{
+  aError = nsContentUtils::CheckQName(aName, false);
+  if (aError.Failed()) {
+    return false;
+  }
+
+  nsAutoString nameToUse;
+  const nsAttrName* name = InternalGetAttrNameFromQName(aName, &nameToUse);
+  if (!name) {
+    if (aForce.WasPassed() && !aForce.Value()) {
+      return false;
+    }
+    RefPtr<nsAtom> nameAtom = NS_AtomizeMainThread(nameToUse);
+    if (!nameAtom) {
+      aError.Throw(NS_ERROR_OUT_OF_MEMORY);
+      return false;
+    }
+    aError = SetAttr(kNameSpaceID_None, nameAtom, EmptyString(), aTriggeringPrincipal, true);
+    return true;
+  }
+  if (aForce.WasPassed() && aForce.Value()) {
+    return true;
+  }
+  // Hold a strong reference here so that the atom or nodeinfo doesn't go
+  // away during UnsetAttr. If it did UnsetAttr would be left with a
+  // dangling pointer as argument without knowing it.
+  nsAttrName tmp(*name);
+
+  aError = UnsetAttr(name->NamespaceID(), name->LocalName(), true);
+  return false;
+}
+
 void
 Element::SetAttribute(const nsAString& aName,
                       const nsAString& aValue,
                       nsIPrincipal* aTriggeringPrincipal,
                       ErrorResult& aError)
 {
   aError = nsContentUtils::CheckQName(aName, false);
   if (aError.Failed()) {

--- a/dom/base/Element.h
+++ b/dom/base/Element.h
@@ -1096,16 +1096,18 @@ public:
     GetAttribute(aName, str);
     str.ToString(aReturn);
   }
 
   void GetAttribute(const nsAString& aName, DOMString& aReturn);
   void GetAttributeNS(const nsAString& aNamespaceURI,
                       const nsAString& aLocalName,
                       nsAString& aReturn);
+  bool ToggleAttribute(const nsAString& aName, const Optional<bool>& aForce,
+                       nsIPrincipal* aTriggeringPrincipal, ErrorResult& aError);
   void SetAttribute(const nsAString& aName, const nsAString& aValue,
                     nsIPrincipal* aTriggeringPrincipal, ErrorResult& aError);
   void SetAttributeNS(const nsAString& aNamespaceURI,
                       const nsAString& aLocalName,
                       const nsAString& aValue,
                       nsIPrincipal* aTriggeringPrincipal,
                       ErrorResult& aError);
   void SetAttribute(const nsAString& aName, const nsAString& aValue,

--- a/dom/webidl/Element.webidl
+++ b/dom/webidl/Element.webidl
@@ -36,16 +36,18 @@ interface Element : Node {
   readonly attribute NamedNodeMap attributes;
   [Pure]
   sequence<DOMString> getAttributeNames();
   [Pure]
   DOMString? getAttribute(DOMString name);
   [Pure]
   DOMString? getAttributeNS(DOMString? namespace, DOMString localName);
   [CEReactions, NeedsSubjectPrincipal=NonSystem, Throws]
+  boolean toggleAttribute(DOMString name, optional boolean force);
+  [CEReactions, NeedsSubjectPrincipal=NonSystem, Throws]
   void setAttribute(DOMString name, DOMString value);
   [CEReactions, NeedsSubjectPrincipal=NonSystem, Throws]
   void setAttributeNS(DOMString? namespace, DOMString name, DOMString value);
   [CEReactions, Throws]
   void removeAttribute(DOMString name);
   [CEReactions, Throws]
   void removeAttributeNS(DOMString? namespace, DOMString localName);
   [Pure]

--- a/testing/web-platform/tests/interfaces/dom.idl
+++ b/testing/web-platform/tests/interfaces/dom.idl
@@ -355,16 +355,17 @@ interface Element : Node {
   [SameObject] readonly attribute NamedNodeMap attributes;
   sequence<DOMString> getAttributeNames();
   DOMString? getAttribute(DOMString qualifiedName);
   DOMString? getAttributeNS(DOMString? namespace, DOMString localName);
   void setAttribute(DOMString qualifiedName, DOMString value);
   void setAttributeNS(DOMString? namespace, DOMString qualifiedName, DOMString value);
   void removeAttribute(DOMString qualifiedName);
   void removeAttributeNS(DOMString? namespace, DOMString localName);
+  boolean toggleAttribute(DOMString qualifiedName, optional boolean force);
   boolean hasAttribute(DOMString qualifiedName);
   boolean hasAttributeNS(DOMString? namespace, DOMString localName);
 
   Attr? getAttributeNode(DOMString qualifiedName);
   Attr? getAttributeNodeNS(DOMString? namespace, DOMString localName);
   Attr? setAttributeNode(Attr attr);
   Attr? setAttributeNodeNS(Attr attr);
   Attr removeAttributeNode(Attr attr);